Capt. Robert O’Donnell of the Stoughton Fire Department ran toward the smoke and fire just as people began running away from where explosions had just occurred near the Boston Marathon finish line. What he found, he said, resembled a battlefield. Dozens of bombing victims – people of all ages – surrounded him.

Capt. Robert O’Donnell of the Stoughton Fire Department ran toward the smoke and fire just as people began running away from where explosions had just occurred near the Boston Marathon finish line.

What he found, he said, resembled a battlefield. Dozens of bombing victims – people of all ages – surrounded him.

“Most of them had amputated limbs – arms, legs,” O’Donnell, 56, recalled during a telephone interview from Boston Monday. “You were actually walking through blood to get to them. I just never had seen anything like it.”

Some people were on fire and crying for help, he said.

“I actually took some pants off a guy; they were still smoldering,” he said. “He was still burning.”

Emergency responders began arriving, and victims were placed into wheelchairs and onto boards. O’Donnell moved quickly from victim to victim, putting tourniquets on as many as he could.

“The whole time, I felt that my son was possibly in the area of that secondary explosion,” O’Donnell said, crying. “I was afraid for my son’s life.”

Robert O’Donnell III, 19, of Easton, a college student who raised nearly $7,500 for Children’s Hospital in Boston before running the marathon, was nearing the finish line when the blasts occurred.

“But there was nothing I could do about that,” the fire captain said. “I had to take care of the people that were there.”

O’Donnell, who was standing on bleachers across from where the explosions occurred, said he knew the situation was bad when he saw the fire and smoke. He said he jumped a fence that separated him from scores of victims.

At first, Boston police and fire officials wouldn’t let him through, but then O’Donnell identified himself as a firefighter and paramedic.

O’Donnell, who has worked as a firefighter for more than three decades, said he had seen his share of bad accidents but had never been in a mass-casualty situation anything like the one Monday.

“So many people were holding onto each other, thinking it was their final moments,” he said.

O’Donnell said he helped load dozens of victims into ambulances.

“I came across at least one that was dead,” he said.

When Boston Fire Department Ladder 26 arrived, it provided a barrier near O’Donnell and other emergency personnel – protection in case there were more explosions, he said.

O’Donnell said the best of Boston came out Monday in the aftermath of the blasts.

“Most of the people ran away, but there was a good number that ran right in and got in and did what they could do,” he said.